Protein identification before and after glyphosate exposure in Lolium multiflorum genotypes.

BACKGROUND: Weeds reduce crop yields, and among the methods used to control these plants, the use of chemicals is preferred. However, the repeated application of herbicides with the same mechanism of action selects for resistant populations. The aim of this study was to evaluate glyphosate resistance in Lolium multiflorum (Lam.) and relate the resistance to protein expression in the absence and presence of the herbicide using a metabolic-proteomic approach. RESULTS: Glyphosate resistance was confirmed, with a sevenfold difference in resistance between susceptible and resistant genotypes. Among the possible mechanisms affecting resistance, mutations in the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), herbicide differential translocation and overexpression of EPSPS are suggested. Susceptible plants had higher growth than did resistant plants in the absence of the herbicide, in addition to greater expression of protein groups related to photosynthesis and to tolerance to biotic and abiotic stresses. With application of glyphosate, resistant plants maintained their metabolism and began to express EPSPS and other candidate proteins related to herbicide resistance. CONCLUSIONS: In the absence of glyphosate, the susceptible plants would replace the resistant plants over time, and abiotic or biotic stresses would accelerate this process. Resistance in plants resulted from a combination of target-site and non-target-site resistance mechanisms. We identified several candidate proteins that could be investigated in future studies on glyphosate resistance. © 2017 Society of Chemical Industry.

Chemical evidence for the effect of Urochloa ruziziensis on glyphosate-resistant soybeans.

BACKGROUND: Soybean (Glycine max) is an important oleaginous legume that has been cultivated in new areas in Brazil, including pastures. Problems of reduced production yields have been reported by soybean growers when the crop is sown immediately after desiccation of pastures of Urochloa spp. using glyphosate. The objective of this work was to extract, isolate and identify the major chemicals from U. ruziziensis that have phytotoxic activity and to evaluate the possible relation between this effect and reduced soybean yield. RESULTS: U. ruziziensis plants at the flowering stage were desiccated using glyphosate at 1.44 kg ha-1 . The plants were collected between five and ten days after treatment. Extracts of dried and ground shoots were obtained by sequential extraction with hexane, dichloromethane and methanol. The results of wheat coleoptile bioassays indicated that the methanol extract was more inhibitory than the dichloromethane extract regardless of glyphosate application. CONCLUSION: Protodioscin, a steroidal saponin, was isolated from the extract as the major component and the activities of this compound were in good agreement with those found for the extract. The release of this compound into the soil is a plausible explanation for the decrease in production observed in transgenic soybean crop after desiccation of U. ruziziensis. © 2017 Society of Chemical Industry.